A Space Division Multiple Access (SDMA) generally refers to a technology of resource multiplexing through spatial isolation between users, that is, an eNB allocates the same resource to users in different separate spaces to thereby improve a utilization ratio of the resource and enhance greatly the throughput of the system and a data transmission rate of the users.
The SDMA technology can be applied widely to indoor and outdoor scenarios to thereby improve the capacity of a cell, data transmission rate and the spectrum utilization ratio of a system and also enhance the performance of coverage in special scenarios, for example, space division multiplexing indoors across floors can multiplex the same resource for users across the floors to thereby improve greatly the capacity of the system while reducing the number of cell handovers for a user climbing up and down the floors. In another example, space division multiplexing applied outdoors to the coverage of an express railway can reduce the number of frequent cell handovers in a short period of time due to mobility at a high speed to thereby improve effectively the coverage performance of the system.
An Evolved Node B (eNB) is a distributed base station equipment which is constituted of a Building Base band Unit (BBU) and Radio Remote Units (RRUs), i.e., an eNB is a base station combination which can be deployed flexibly in a distributed way.
The BBU is a part of the eNB responsible for processing data and deciding transmission data on each RRU. The RRU is a radio frequency transmission part of the eNB, each separate space has one corresponding RRU, one RRU can support data transmission on one or more channels, and each channel can be connected with one or more antennas, but data on a plurality of antennas on the same channel is combined for transmission. The number of channels in each separate space depends upon practical networking. Only single-port transmission can be performed when a single channel is configured in each separate space and multi-port transmission modes via two ports, four ports, etc., can be adopted when a plurality of ports are configured in each separate space. The BBU and the RRUs are connected together through optical fibers, and one BBU can process data on a plurality of RRUs concurrently. The processing power of the BBU depends upon the processing power and number of boards in the BBU and determines the number of RRUs that can be connected with the BBU.
An implementation of the SDMA technology requires a specific isolation requirement to be satisfied between the different RRUs, and isolation is achieved for the indoor SDMA generally through a penetrating loss across floors while isolation can be achieved outdoors through antenna orientation and a physical distance (e.g., street coverage, a cross-road or a fork-road, an express railway, etc.)
Essentially the SDMA technology is to perform space division multiplexing through spatial isolation between the different RRUs and to allocate the same resources to users served by the different RRUs. Ideally the throughput of the system increases constantly with an increasing multiplexing number and has an upper limit dependent upon the practical processing power of the BBU.
Taking as an example a BBU connected with a number L of RRUs where the different RRUs are intended for different floors, a signal processing model of the BBU and the RRUs is as illustrated in FIG. 1, where each RRU may receive a signal transmitted from a user, and a measuring module decides (an) RRU(s) serving the user by comparing received signal strengths of the signal transmitted from the user on the respective RRUs and submits serving information to a scheduling module; the scheduling module allocates resources to users at the respective floors by pairing the SDMA-enabled users served by the different RRUs and allocating the same resources to the paired users and also transmits pairing information and scheduling information to the measuring module and a data receiving module for next reception of a signal; and the measuring module transports corresponding measurement data to the data receiving module according to the previous pairing information for detection of user data. Also the scheduling module transports the current pairing information and scheduling information to the data receiving module for determination of transmission data on each RRU.
The Multiple User-Multiple Input Multiple Output (MU-MIMO) scheme is adopted for space division multiplexing of an existing LTE or LTE-A system, and since interference cancellation is required at a transmitter, a pre-coding algorithm of the scheme is highly complex; and since different beams formed on a plurality of antennas in the MU-MIMO are to be aimed at several paired users respectively, this scheme is inappropriate in a distributed antenna scenario with large spatial isolation between the antennas.
There are a variety of physical channels and physical signals dependent upon the types of data transmitted at a physical layer in the LTE and LTE-A systems. Different resource allocation schemes are adopted for the different physical channels and physical signals, and resource locations of a part of the channels are associated with each other, thus resulting in the feasibility and an implementation solution thereof with the SDMA. With the technology of space division multiplexing, space division multiplexing schemes of the respective channels have to be determined for the system. The existing algorithm supports a limited number of paired users with the MU-MIMO and can only be applicable to a data channel.